had the same problem but intermittent. change thermostat.

 

I know this is an old thread and have read the related link to this problem/fix. But here goes ......
Recently purchased the HHR 4-19-13 from a reputable dealer, within 150 miles the code to replace the thermostat showed up. Took the car back and they cleared the code and changed the part while we waited. Today the code appeared again, gauge went dead and ac blowing hot. Returned to the dealer and they replaced the sending unit AND another thermostat.
Well guess what,same thing happens again. Gauges stop working and ac blowing hot. Scanner at auto zone says p0128 (thermostat stuck) . The young man instructs us the remove the red fuse at the battery for a few minutes and replace it. Start the HHR and the gauge works and is reading 187F and ac blowing cold again.
The young man tells my husband and I to remove the radiator cap after it cools. Start the engine and allow it the rise to operating temp. When the water begins to move through the raditor the thermostat is open and water is circulating.
We did just that and the water is moving through the radiator. We used a cooking thermometer at the radiator and it is reading 182 F. And once again the temp gauge is flat and code P0128 is showing.
Our conclusion is that the termostat functions from the visual of the fluid circulating.The senson has also been replaced by our dealers mechanic.

• Could this problem a bad connection at the sending unit?

• Second question is do you know of the fix ?

Our dealer is on the hook for the repairs. The car must pass emmisions before they can issue a tag and registration here in Atlanta.As long as any code appears when on the machine when testing is underway, the unit fails the cars emmision testing. Also you must have registered 150 miles after a code clearing to get a retest.
Becky and Greg

 

Welcome to the site.
Code P0128 does not define as "stuck thermostat". It is the code for the operating temp being too low. Most times it is because the thermostat is stuck open not allowing the engine to heat up quick enough. If it doesn't heat up in the computers time frame(?) it throws the code and shuts down the AC.
If they replaced the thermostat and sending unit, it sounds like a wiring issue. Could just be a loose connection. Where? Not sure. Tracing down wiring problems can be a pain.
One question. When you were checking the radiator for water flow, how long did it take to warm up?

 

Well, it did seem to take about 4 to 5 minutes before it began to flow.
Thanks for the reply. Also I will get a closer look at the area the work was allegdly performed on her ride. It may just as well be stuck open and taking too long to heat up.
Thanks for your reply. I will do a follow up on the fix . It will be Wenesday when it is returned for the repair "again".
Us

 

If it is stuck open, it would be circulating(flowing) as soon as you start the engine. 4-5 minutes at idle seems a little fast to reach operating temp. Then again maybe not. Not exactly sure. Haven't ever timed mine.
Some past posts have mentioned that the old thermostat can leave behind part of the rubber seal in the coolant. This old seal can then become wedged in the new thermostat, thus leaving it stuck open.
Just trying to cover the possibilities. Let us know what you find.

 

I still owe Wopper $0.37 as he said my therostat needed to be replaced he was right. where do i send it???

 

No problem - hang onto it for now - I'll call you when I am homeless.

 

It is repaired. Therm stuck open with a small amout trash. The mechanic showed it to her. Now the operating temp is at 203 F , right where it likes it.
Thanks for replys .....

 

Good deal - glad it is fixed. And firemangeorge - GOOD CALL on the debris!!!! A good flush of the system might be a wise choice when replacing the thermostat if the gasket is badly deteriorated, and is missing pieces of the gasket.

 

Whopper may you never be homeless, so now Im $0.37 richer.